The proposed research is concerned with a comprehensive study of the glomerular mesangium. The influence of hemodynamic and physiologic factors on mesangial uptake and disposal of aggregated IgG will be evaluated in the rat. Ultrastructural, immunoelectron microscopic and sterologic techniques will be employed in evaluating the transport of macromolecules through the mesangial region with particular emphasis on the efferent limb. The role of charge of the macromolecule in regulating the traffic into and out of the mesangium will be evaluated by using tritiated neutral, anionic and cationic dextrans.